Evidence perhaps of defective heating in sleeping area and rodents (7)
I believe the answer is:
dormice
'rodents' is the definition.
(dormouse is a kind of rodent)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for dormice that I've seen before include "creatures" , "For these heavy sleepers" , "Furry animals" , "Little hibernating rodents" , "Small field rodents" .)